North Korean leader Kim Jong-un has received a personal letter from US President Donald Trump, the country's official Korean Central News Agency reported on Sunday.

After reading the letter, Kim "said with satisfaction that the letter is of excellent content," the report said. Kim said he would "seriously contemplate the interesting content."   

But the agency did not disclose more details about the content of the letter.  

Talks between the two countries have been slowed down since the second summit between the two leaders in February that ended without reaching an agreement. The two sides have blamed each other for the breakdown but both have expressed a willingness to meet again, with Trump saying earlier this month that he had received a "beautiful letter" from Kim.

South Korea's presidential Blue House said it was aware of the correspondence through its communication with Washington, and described the exchange as "positive."

Analysts say the North's apparently friendly overtures to Trump signaled that Pyongyang was ready to break the deadlock with Washington.

Trump and Kim held a groundbreaking summit in Singapore last year - the first-ever meeting between a North Korean leader and a sitting US president - where the pair signed a vaguely-worded deal on denuclearization.

But in Hanoi this year, Washington accused Pyongyang of effectively demanding an end to all sanctions for partial disarmament, while the North said it wanted some measures eased in return for closing all the nuclear facilities at its Yongbyon complex.

Since then, Pyongyang has accused Washington of acting in "bad faith" and given it until the end of the year to change its approach.

Yang Moo-jin, a professor at the University of North Korean Studies, said the written correspondence between the leaders was "very meaningful."

"The letter diplomacy shows they are communicating even though there is a lull in talks," Yang said.

This is not the first time the two leaders have opted for more traditional means of communication.

Less than a month before the Singapore summit, Trump wrote to Kim, telling the North's leader not to "hesitate to call me or write."